There is growing interest in developing novel foods containing probiotic microorganisms. Probiotics are commonly defined as viable microorganisms (bacteria or yeasts) which, when administered in adequate amounts, confer a health benefit on the host.
To deliver the health benefits, probiotics need to contain an adequate quantity of live bacteria capable of surviving the acidic conditions of the upper gastro-intestinal tract as well as proliferating in the intestine, a requirement that is not always fulfilled. A daily dose of at least 109 live cells per portion has been assumed by IPA Europe to be sufficient according to the literature available, although a different dose per strain could be also acceptable if substantiated by specific studies. However, monitoring the survival of the probiotic cultures in foods is hampered by the lack of accurate, reliable, convenient and sensitive identification methods, with the ability to distinguish the strains of interest among other closely related microorganisms present in the products.
Insertion of beneficial bacteria into a food matrix presents a totally new challenge, not only because of their interactions with other constituents, but also because of the severe conditions often employed during food processing and storage, which might lead to important losses in viability. To overcome such deficiencies, immobilisation techniques have been proposed, aiming at stabilisation of cells and formulation of new types of foods fortified with immobilised health-promoting bacteria that are only released upon reaching the human gut.
Our research has focused on marketable ‘ready-to-use’ functional dried immobilised probiotic cultures, suitable for the production of food products. In this vein, a process for the effective immobilisation of probiotic cells on natural, food-grade, prebiotic supports was developed. Cell immobilisation enhanced cell viability, extending the shelf-life of the final product, as probiotic strains were encountered at levels greater than 7 logcfu/g after 2 months of storage at ambient temperature, while no contamination was noted. Similar levels of living cells were also obtained after 6 months of storage at 4oC and after 12 months at -18oC. In vitro studies showed that immobilisation technology enhanced cell viability when exposed to acidic environments similar to those of the gastrointestinal tract. Similar results were obtained by in vivo experiments in mice where Lactobacillus casei cells were shown to survive the digestion process and colonised the gastrointestinal tract, modulating the gut microbiome with subsequent antineoplastic properties. Dried immobilised cells, produced by our method, are easy to use by the food industry both at room temperature and at 4 and -18oC processes, and can also withstand high temperature processing steps (up to 60oC) with no significant losses. Our process was used in a pilot scale to produce ice-cream containing probiotic cultures at concentrations greater than 7 logcfu/g. Cells remained at such high levels even after 12 month of storage at -18oC.
Our process resulted in successful dried immobilised probiotic culture preparations suitable for many food applications that maintained cell viability during storage for time periods suitable for industrial uses.